Absolute structure and total synthesis of lipogrammistin-A, a lipophilic ichthyotoxin of the soapfish

Lipogrammistin-A (Ib) was isolated as an ichthyotoxic and hemolytic constituent of the skin mucus of the grammistid fish Aulacocephalus temmincki. Its absolute stereochemistry was established by chemical degradation and total synthesis. The stereochemistry of the 2-methylbutyryl moieties attached to N9 and N15 was determined to be S by HPLC analysis of a diastereomeric derivative. The stereochemistry of the remaining C4 position was elucidated to be S by a total synthesis of the two diastereomers (4S)- and (4R)-1.